Elastic Laminates and Methods of Manufacturing Same

ABSTRACT

A method for forming an elastic laminate comprising: bonding a first nonwoven to an elastic film to form a laminate; activating the laminate to form an activated laminate; and bonding a consolidated nonwoven to the elastic film of the activated laminate to form the elastic laminate.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/740,036, filed Nov. 28, 2005, which is hereby incorporated byreference.

FIELD OF INVENTION

The present invention relates generally to elastic laminates and theirmethods of manufacture, and, more particularly, to breathable elasticlaminates having nonwoven surfaces on both sides.

BACKGROUND OF INVENTION

Breathable elastic laminates are used in the manufacture of many goods,including, for example, disposable articles such as diapers, femininesanitary articles, and bandages. These applications require that thelaminate be strong, stretchable, and soft to the touch. Improving one ofthese features, however, tends to diminish the others. Consequently,previously-introduced laminates tend to represent a compromise amongsoftness, elasticity, and strength.

For example, one prior art laminate comprises an apertured elasticlaminate produced by vacuum laminating a carded polypropylene nonwovento a multilayer coextruded elastic film. The laminate is then activatedin the cross direction using intermeshing gears. This construction hasthe advantage of a soft feel, but is limited to two layers (nonwoven andfilm) and lacks high peel strength.

Another prior art product comprises an apertured elastic film which isactivated in the cross direction (CD) and is ultrasonically bonded oneach side to a consolidated nonwoven. Although this laminate tends to bestrong, it has a harsher feel than desired, requires substantialultrasonic energy to bond the layers, and, because it has three layers,it tends to lack the level of stretch obtainable from a laminate withjust a single layer of nonwoven.

Therefore, there is a need for a breathable laminate that is soft oneither side yet stretchable and strong. The present invention fulfillsthis need among others.

SUMMARY OF INVENTION

The invention relates to an elastic laminate having soft, nonwovensurfaces on both sides, yet is stretchable and strong. Specifically, theelastic laminate comprises an elastic inner layer and two outer nonwovenlayers, in which each nonwoven layer is rendered extensible through adifferent method. That is, one nonwoven layer is activated, while theother is consolidated.

Applicants have discovered unexpectedly that the laminate of the presentinvention has an exceptional degree of cross direction stretch, offers apleasant, soft feel, and can be bonded ultrasonically at full line speedto obtain an exceptionally strong interlayer bond. Without being boundto any particular theory, applicants hypothesize that the high level ofstretch results from “elasticizing” the two nonwoven layers using twodifferent techniques—i.e., activation and consolidation. This approachsynergistically combines the strengths of the two technologies,resulting in a laminate having the high tensile strength and a strongbond characteristic of a consolidated/ultrasonically bonded nonwoven,and the softness and tear resistance characteristic of an activatednonwoven. Furthermore, this approach appears to minimize the observedtendency of one nonwoven layer to constrain the extensibility of theother nonwoven layer in the same laminate.

Accordingly, one aspect of the invention is an elastic laminate havingtwo outer nonwoven layers which are rendered extensible using twodifferent techniques. In a preferred embodiment, the elastic laminatecomprises: (1) an elastic layer having a first and second side; (2) anactivated nonwoven layer bonded to the elastic layer on the first side;and (3) a consolidated nonwoven layer bonded to the elastic layer on thesecond side.

Another aspect of the invention is a method for producing the laminatedescribed above. In a preferred embodiment, the method comprises: (1)bonding a first nonwoven to an elastic film to form a laminate; (2)activating the laminate to form an activated laminate; and (3) bonding aconsolidated nonwoven to the elastic film of the activated laminate toform the elastic laminate.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic view of an elastic laminate of the presentinvention.

FIG. 2 shows a schematic of a manufacturing line for making the elasticlaminate of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to an elastic laminate and a method formaking it. Briefly, referring to FIG. 1, the elastic laminate 10comprises an elastic layer 12 having a first and second side, 14, and15. Preferably, but not necessarily, the elastic layer has apertures 13or is otherwise modified to be breathable. On the first side 14 is anactivated nonwoven layer 16 bonded to the elastic film material 12. Asused herein the terms “activated” or “activation” refer to a method orstate in which a laminate comprising an elastic layer and at least oneless-elastic layer is stretched to an extension limit beyond thedeformation point of the less-elastic layer to allow the elastic layerto elongate to the extension limit essentially unimpeded by theless-elastic layer. Activation is a well-known technique. On the secondside 15 is a consolidated nonwoven layer 17 bonded to the elastomer film12. As used herein, the terms “consolidated” or “consolidation” refer toa method or state in which the fibers or fiber-like elements of thenonwoven are aligned, thereby allowing the nonwoven to elongate in adirection perpendicular to the alignment. Consolidation, likeactivation, is a well-known technique for imparting extensibility to anonwoven.

Referring to FIG. 2, the method 100 of preparing the laminate 10 isdescribed in connection with a preferred manufacturing apparatus. Themethod comprises bonding a first nonwoven 50 to an elastic film 60 toform a laminate 65. The elastic film is optionally breathable. Once thelaminate 65 is formed, it is activated to form an activated laminate 75.A consolidated nonwoven 55 is then bonded to the elastic film 50 of theactivated laminate 75 to form the elastic laminate 95. The elasticlaminate 95, its uses, and the method of preparing it are described indetail below.

Referring back to FIG. 1, the elastic layer 12 provides elasticity tothe laminate. The elastic layer comprises at least one elastic material.Suitable elastic materials include any material that is capable of beingformed into a thin sheet, rendered breathable and bonded to nonwovens.For example, elastic materials include natural and/or syntheticpolymeric materials including isoprenes, butadiene-styrene materials,styrene block copolymers (e.g., styrene/isoprene/styrene (SIS),styrene/butadiene/styrene (SBS), or styrene/ethylene-butadiene/styrene(SEBS)), olefinic elastomers, polyether esters, polyurethanes, etc. Incertain preferred embodiments, the elastic materials may comprise highperformance elastic material such as Kraton® elastic resins from KratonPolymers, LLC, which are elastic block copolymers.

The form of an elastic layer 12 can vary and may include, for example,elastic strands, elastic nonwoven, elastic film, elastic adhesive,elastic tacky polymeric web, elastic scrim, etc. For the sake ofsimplicity, unless otherwise noted, these different forms are referredto collectively herein as “elastic film.” In certain preferredembodiments, a monolayer elastic film is used. It should be understood,however, that the present invention in not limited to a monolayer filmand, in certain applications, a film having multiple layers may be used.For example, it may be advantageous to have an elastic core between twoskin layers to enhance bonding to the nonwoven layers or to facilitateprocessability. Suitable skin layers are well known and include, forexample, polyethylene which may be more or less elastic than the elasticmaterial. The thickness of the elastic film may vary according to theapplication, although the individual layers of the films are typicallythin (e.g., the elastic core is usually, but not necessarily, less than100 microns, and skin layers, if used, are usually less than 20microns).

Preferably, the elastic film is breathable or is modified to bebreathable in conventional ways. Such ways include, for example,aperturing, slitting, or impregnating with granular particles to createmicrovoids upon stretching of the elastic film.

The first nonwoven layer 16 provides a soft and breathable surface onceactivated (discussed below) on the first side 14 of the elastic layer.Suitable nonwovens are capable of being activated and are less elasticthan the elastic layer 12. Suitable nonwovens include loose fibers andwebs prepared using know techniques such as, for example, air laying,spun bond, spun lace, bonded melt blown, thermobond, bonded carded. Thenonwoven material may be homogeneous or contain a variety of wovenmaterials including bi-component fibers (e.g. having an inner core ofone material and an outer core of a second material), fibers ofdifferent morphologies, geometries, and surface finishes. Suitablenonwovens materials include, for example, fibrous polyolefins such aspolyethylenes and polypropylenes, and natural fibers such as cotton andcellulose.

The consolidated nonwoven 17, like the first nonwoven 16, provides asoft and breathable covering to the second side 15 of the elastic layer12. Unlike the first nonwoven, the consolidated nonwoven is renderedextensible through a consolidation method rather than an activationmethod. The consolidation method is discussed in detail below.

The laminate 10 may be used in any application requiring a soft,stretchable, breathable material, and especially well suited fordisposable articles given its relatively low cost. Suitable applicationsinclude, for example, absorbent articles, including adult, child orinfant incontinent products (diapers, including parts such as diaperears, tabs, and/or side panels, briefs, etc.); wraps, including sterileand nonsterile (e.g. bandages with and without absorbent sections,) aswell as other disposable and/or multiple use products; e.g., articlesproximate to a human or animal body, such as (e.g., garments, apparel,including undergarments, under- and outer-wear, for example,undershirts, bras, briefs, panties, etc., bathing suits, overalls,socks, head coverings and bands, hats, mitten and glove liners, medicalclothing, etc.) bed sheets; medical drapes; packaging materials;protective covers; household; office; medical or construction materials;wrapping materials; etc. therapeutic devices and wraps.

The method of making the laminate is described below with reference toFIG. 2. FIG. 2 shows elastic source 20 for providing elastic film 60. Inthis embodiment, the elastic source 20 comprises a slot die or blown diefor extruding molten or semimolten elastic material or coextrudingmultiple layer film structure in which one or more of the layers areelastic. It should be understood, however, that any conventional elasticsource may be used, including, for example, a roll of elastic material.

The first nonwoven source 70 provides the first nonwoven 50. In thisembodiment, the first nonwoven source 70 comprises a roll of material,however, any suitable source may be used, including forming the materialin situ.

The first nonwoven 50 is brought into contact with elastic film 60 andbonded thereto. In this embodiment, the molten or semimolten phase ofelastic film 60 facilitates bonding with the first nonwoven 50. Thefirst nonwoven 50 may also be bound, in whole or part, to the elasticlayer using other conventional methods, such as hot pin aperturing,adhesive bonding, thermal bonding, ultrasonic bonding, and combinationthereof.

Optionally, the elastic film 60 is modified to render it breathable. Onepreferred approach for aperturing the elastic layer is shown in FIG. 2in which a pressure differential source 30 is used. Specifically, thefirst nonwoven 50 and the elastic film 60 are provided to pressuredifferential source 30 such that the elastic film 60 is interposedbetween the pressure differential source 30 and the first nonwoven 50.Pressure differential source 30 creates a pressure differential acrossthe thickness of the laminate which is high enough to cause ruptures(i.e., apertures) in the elastic film 60. This method createsthree-dimensional apertures which are especially preferred wherebreathability or permeability of the laminate is desired.

The pressure differential source 30 is well known. In a preferredembodiment, the pressure differential source 30 comprises a vacuum (notshown) and an aperture definition device 120. In this embodiment,aperture definition device 120 comprises a screen with 20 apertures perlinear inch in a square pattern, referred to herein as 20 square. Otherscreen geometries may be used to vary the amount of open area, aperturesize, geometries, patterns, and other attributes. Furthermore, more thanone aperture definition device may be used, for example, a device in onearea may provide one pattern of apertures, and a device in another areamay provide another desired pattern.

In certain embodiments, it may be desired to modify the elastic layer tomake it breathable before it is bonded to the first nonwoven layer.Furthermore, it may preferable to use other known aperturing techniquessuch as pin rolls, slitting, hydrojets, or lasers, instead of or inaddition to a pressure differential source to impart permeability orbreathability to the laminate. It should also be understood thatmodifying the elastic film to render it breathable is not required ifthe elastic film comprises elastic strands or scrim in which case it isalready breathable.

Pressure source 35 provides pressure to the materials. A nip roll isused in the preferred embodiments, although any suitable source may beused as a pressure source. Additionally, some embodiments may dispensewith a pressure source, or use a pressure differential source as apressure source as well. Moreover, pressure source 35 is shown hereupstream of the pressure differential source, although it may be locatedadjacent to the pressure differential source 30 or down stream of thepressure differential source 30.

Once the elastic layer is bound to the first nonwoven, it is activated.Referring back to FIG. 2, the laminate 65 is activated in an activationarea 40. The activation area 40, in a preferred embodiment, involvesintermeshing gear (“IMG”) activation, although any conventionalactivation technique may be used. In the embodiment shown in FIG. 2,activation occurs in the transverse or cross direction (CD), althoughactivation may be in any direction desired, e.g., machine direction(MD), diagonally, or a combination of directions. Further, activationmay occur along the entire laminate or only in predetermined areas ofthe laminate. In other embodiments, the degree of activation may bevaried, for example, a lightly activated area may be used to give alaminate low elasticity, while a heavily activated area may be used togive a laminate high elasticity. Of course, activated regions may beinterposed with nonactivated regions as well, to provide zones orregions of extensibility to the laminate.

Returning now to the embodiment of FIG. 1, second nonwoven source 80provides a second nonwoven 55. In this embodiment, the second nonwovensource 80 comprises a roll of material, although any suitable nonwovensource may be used, such as forming the material in situ.

In one embodiment, the second nonwoven 55 is consolidated on-line.Consolidation may be performed using various techniques such as heatconsolation, cold drawing, or combing. Preferably, heat consolidation isused which is disclosed, for example, in U.S. Pat. No. RE 35,206, whichis hereby incorporated by reference. As shown in FIG. 2, the secondnonwoven 55 passes through heat application area 45, where heat isapplied, and the fibers of the web are oriented in the machinedirection, thereby providing for elongation in the cross direction.Although consolidation is performed on-line in this embodiment, itshould be understood that the consolidation may be performed ahead oftime, and a source of consolidated nonwoven be provided to the line.

The consolidated nonwoven 91 is brought into contact with activatedlaminate 75 through rollers 81 and 82 and bonded using known techniques.Preferably, the consolidated nonwoven 91 and laminate 75 are bondedultrasonically in the ultrasonic bonding area 85. It has been found thatthis bonding can be performed quickly at normal line speeds, e.g., 70mpm.

Varying the materials and method conditions may vary the characteristicsof the laminate. For example, selection of particular elastic and/ornonwovens, or selective processing of those materials, can result inoptimization of desired properties such as bond strength, softness,elasticity, breathability, etc. Examples of method variables that may beused to modify laminate characteristics include modifying the phase ofthe elastic layer prior to bonding; modifying the pressure differentialapplied by a pressure differential source; modifying pressure imposed bya pressure source; modifying apertures in a nonwoven; modifyingapertures provided in an aperture definition device; various secondarytreatments of the laminate and/or components of the laminate (e.g.plasma treatment), modifying stretching of a laminate followinglamination, and combinations thereof. A laminate may also be modified inany suitable fashion, for example, a laminate may be sewn, bonded,printed, cut, shaped, glued, fluted, sterilized, etc.

Although the present invention has been described with respect tovarious specific embodiments, various modifications will be apparentfrom the present disclosure and are intended to be within the scope ofthe following claims.

1. A method for forming an elastic laminate comprising: bonding a firstnonwoven to an elastic film to form a laminate; activating said laminateto form an activated laminate; and bonding a consolidated nonwoven tosaid elastic film of said activated laminate to form said elasticlaminate.
 2. The method of claim 1, wherein said elastic film isapertured.
 3. The method of claim 2, wherein said elastic film is bondedto said first nonwoven and apertured essentially simultaneously.
 4. Themethod of claim 3, wherein said first nonwoven and said elastic film areapertured essentially simultaneously.
 5. The method of claim 3, whereinvacuum lamination is used to bond said first nonwoven to said elasticfilm and to aperture said elastic film.
 6. The method of claim 2 whereinthe elastic film is apertured after the first bonding step.
 7. Themethod of claim 2, wherein the elastic film is apertured before thefirst bonding step.
 8. The method of claim 1, wherein activating saidlaminate comprises activating said laminate in the cross direction. 9.The method of claim 8, wherein said laminate is activated usingintermeshing gear activation.
 10. The method of claim 1, wherein saidconsolidated nonwoven is extensible in said cross direction.
 11. Themethod of claim 1, wherein at least one of said bonding steps comprisesultrasonic bonding.
 12. The method of claim 11, wherein said bonding ofsaid consolidated nonwoven is performed ultrasonically.
 13. The methodof claim 1, wherein said bonding of said consolidated nonwoven isperformed at essentially the same line speed as said activation step.14. An elastic laminate comprising: an elastic layer having a first sideand a second side; an activated nonwoven layer bonded to said elasticlayer on said first side; and a consolidated nonwoven layer bonded tosaid elastic layer on said second side.
 15. The elastic laminate ofclaim 14, wherein said elastic layer is breathable.
 16. The elasticlaminate of claim 15, wherein said elastic layer is apertured.
 17. Theelastic laminate of claim 14, wherein said activated nonwoven layer is acarded nonwoven.
 18. The elastic laminate of claim 17, wherein saidactivated nonwoven layer is polypropylene.
 19. The elastic laminate ofclaim 14, wherein said activated nonwoven layer is extensible in a firstdirection, and said consolidated nonwoven layer is extensible in saidfirst direction.